40 



FOUNDATIONS OF BIOLOGY 



of forming a single body as it does in most cells, in Parame- 

 ,cium is distributed in two parts: a larger body, or MACRO- 

 NUCLEUS, and a smaller body, or MiCRONUCLEUS. 1 Strictly 



speaking, the macronucleus and 

 micronucleus together constitute 

 the nucleus of the cell, and rep- 

 resent a sort of physiological 

 division of labor in the chromatin 

 complex. But it is in the cyto- 

 plasm that specialization is most 

 conspicuous. Not only are there 

 general differentiations into ecto- 

 plasm and endoplasm, but these 

 regions also have local speciali- 

 zations such as CILIA for loco- 

 motion, TRICHOCYSTS for defense, 



PERISTOME, MOUTH, and GULLET 



for the intake of solid food, 

 GASTRIC VACUOLES for digestion, 

 and CONTRACTILE VACUOLES for 

 excretion. And withal, recent in- 

 vestigations indicate that various 

 parts of the cell are coordinated 

 by a 'neuromotor' apparatus. 

 (Fig. 10.) 



Paramecium, under favorable 

 conditions, grows rapidly and, 

 when it has attained the size limit characteristic of the 

 species, cell division takes place, with the result that from 

 the single large cell there are formed two smaller individuals 

 which soon become complete in all respects. These, in turn, 



FIG. 10. Paramecium calkinsi. 

 Diagrammatic, a, contractile vac- 

 uole surrounded by radiating 

 canals; b, macronxicleus; c, mouth; 

 d, undulating membrane extending 

 lengthwise in gullet; e, gastric 

 vacuole in process of formation, at 

 end of gullet ; /, contractile vacuole, 

 fully formed; g, gastric vacuoles; 

 h, endoplasm; t, micronuclei; j, 

 peristome and peristomial cilia; k, 

 trichocysts in ectoplasm; I. cilia. 



1 The several species of Paramecium differ in regard to micronuclear number; e.g., 

 P. caudatum has one micronucleus, and P. aurelia and P. calkinsi have two micronuclei. 



